SQL

Types of commands in Structured Query Language (SQL):

Data Definition Language (DDL):    Create, Alter, Drop, Truncate, Rename

Data Retrieval Language (DRL):      Select

Data Manipulation Language (DML): Insert, Delete and Update

Data Control Language (DCL):        Grant and Revoke

Transaction Control Language (TCL): Commit, Save point and Rollback

Create Table Command:

                 This command allows you to create a table.

Syntax: CREATE TABLE table_name (Column1  data type null/notnull,column2  data type  null/not null..);

                Each and every column should have a data type.

Creating a table from an existing table:

Syntax: create table table_name as (select * from existing table_name);

Creating a table from the selected columns of an existing table:

Syntax: create table table_name as (select  column1,column2  from existing table_name);

Creating a table definition without the data:

Syntax: create table table_name as (select * from existing table_name where 1=2);

Alter Table Command:

                Alter table command allows you to add, delete and modify the columns in an existing table.

To add a column:

Syntax: alter table table_name add column1 data type;

To modify a column:

Syntax: alter table table_name modify column1 data type;

To delete a column:

Syntax: alter table table_name drop column1;

Drop Command:

The DROP command removes a table from the database. All the tables' rows, indexes and privileges will also be removed.

Syntax: Drop table table_name

Truncate Command:

Truncate is used to delete all the rows from the table and free the space containing the table.

Syntax: truncate table table_name

Rename Command:

This is used to rename an existing table.

Syntax: rename  old_table_name  to new_table_name

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